1. Field of the Invention
The present invention relates to a technique for cleaning elements in a vacuum chamber and, more particularly, to a technique for cleaning a stage, or the like, for holding, for example, a substrate to be processed.
2. Description of the Related Art
In the manufacturing processes of semiconductors or flat panel displays (FPDs) such as liquid crystal displays, a major concern is to prevent substrates, during processing, being contaminated with particles entering from outside the manufacturing equipment or generated within the manufacturing equipment. In particular, if the stage installed in a vacuum chamber is contaminated with particles, the particles may stick to the underside of the substrate mounted thereon, and the contamination may spread in subsequent steps, eventually rendering the final products defective.
FIG. 1 shows a schematic diagram of a conventional plasma etching apparatus. A stage 2, for holding a substrate to be processed, is disposed inside a vacuum chamber 1, and a high-frequency power supply unit 3 as a bias power supply unit is connected via a capacitor 4 to the stage 2 to which is also connected, via a low-pass filter 6, to an electrostatic power supply unit 5 for holding the substrate onto the stage 2. The vacuum chamber is grounded, and its upper surface acts as an upper electrode 7. The surface of the stage 2 is coated with alumina, polyimide, or the like, and the semiconductor substrate is attracted onto it when a DC voltage is applied from the electrostatic power supply unit 5. A focus ring 8 is mounted on the peripheral portion of the stage 2 in such a manner as to encircle the substrate placed thereon. The focus ring is a ring-shaped plate made of a material similar to that of the substrate, for example, and is provided to hold a generated plasma on the substrate. A processing gas is introduced through gas inlet ports 10 of a shower head 9 disposed above the stage. Though not shown here, a pump for partially or wholly evacuating the chamber is provided. In the illustrated example, it is assumed that particles P are left sticking to the stage 2.
When performing processing in the above vacuum chamber, the semiconductor substrate (not shown) is placed on the stage 2, and is held on it by electrostatic attraction by applying a voltage from the electrostatic power supply unit 5; then, a reactive gas for processing is introduced into the chamber 1 through the gas inlet ports 10 of the shower head 9, and a plasma is generated by supplying power from the high-frequency power supply unit 3, to perform a predetermined processing. At this time, if the particles P are left sticking to the stage 2, they stick to the underside of the substrate during processing, and the contamination spreads in subsequent steps, leading to such problems as a reduced production yield of the finally produced semiconductor devices.
Possible sources of such particles include, for example, those entering from outside the chamber, those due to the contact friction between the stage 2 and the semiconductor substrate, and those formed by the deposition of products of the reactive gas. In view of this, Japanese Unexamined Patent Publication No. 2002-100567, for example, proposes a method of keeping the stage clean by cleaning it with a brush scrubber or a wiper blade or by spraying a clean liquid or gas onto the stage.
However, since such cleaning means usually requires opening the lid of the chamber and thus exposing the chamber to the atmosphere, the cleaning itself can cause contamination. Further, using a brush scrubber or a wiper blade under reduced pressure is not effective in removing particles (for examples, particles with particle size of about 10 nm); on the contrary, this runs the risk of generating new particles due to physical friction. On the other hand, cleaning the stage with a liquid requires a complicated structure for cleaning, and greatly reduces throughput. Moreover, by simply spraying a gas, it is difficult to thoroughly clean the stage, because the collision cross section between the particle and the gas is very small.